The start of puberty is caused by the hypothalamus (the part of the brain that controls the pituitary gland). It tells the pituitary gland (a pea-sized gland near the base of the brain) to release hormones (Picture 1). These hormones tell the ovaries in girls to make sex hormones. Some girls start puberty too early for no known reason. It may run in families - mothers and sisters may have also matured early.
Sometimes a problem in the brain, such as injury, a tumor or an infection causes early puberty. A problem in the ovaries or thyroid gland could also start puberty early.
Some girls can have “partial” precocious puberty and may have growth of pubic or underarm hair but no other sexual development. Some girls, usually between the ages of 6 months and 3 years old, may show breast growth that goes away later or may continue without other changes that come with puberty. Children with "partial" early puberty may need to be seen by a doctor.
How It Affects the Child
When puberty is finished, a girl will stop growing. Children with untreated early puberty sometimes do not reach their full adult height, because their bones mature and bone growth stops too soon. Even though they may have an early growth spurt that makes them taller than other children their age, finishing puberty early makes them stop growing too soon. Early puberty can be hard for your child to deal with emotionally and socially. Girls may be confused or embarrassed about having their menstrual periods and breasts before other children. They can be moody and irritable. One of the hardest parts is the teasing that these children sometimes face from others.
Diagnosis
Your child's doctor may order blood tests to check hormone levels. X-rays of your child's hand may be done to see if the bones are growing too fast. Other tests to help rule out specific causes may include: CT scans (see Helping Hand, CT Scan, HH-III-199), MRIs (see Helping Hand, MRI (Magnetic Resonance Imaging), HH-III-69), and ultrasounds (see Helping Hand, Ultra Sound, HH-III-64).
Treatment
Children with precocious puberty can be treated. Doctors can help your child to grow to reach her full adult height and help stop the emotional and social problems she may face from maturing early.
If her doctor thinks your daughter has precocious puberty, she may be sent to a pediatric endocrinologist (a doctor who specializes in growth and hormonal disorders in children). Depending upon the cause, treatment may include:
Treating the underlying cause or disease.
Using medicines to lower the levels of hormones and delay sexual development.
Sometimes no treatment is needed.
Caring for Your Child
Give your child a simple, truthful explanation about what's happening. Explain that these changes are normal for older children and teens, but her body has started developing a little too early. Try not to focus on your child's appearance. Instead, offer praise for achievements in school, sports and other activities. Watch for signs that teasing or other problems may be affecting your child. Warning signs to watch for and talk to her doctor about include:
Poor grades, problems at school
Loss of interest in daily activities
Depression
Reference from: https://www.nationwidechildrens.org/
Good information